The federal government has hired tens of thousands of temporary workers to prepare for the 2010 Census -- a population count that could remake the political map even as the foreclosure crisis makes it more difficult to account for millions of dislocated Americans.

Early analysis indicates that Texas will likely be the biggest winner since the prior count a decade ago, picking up three or four seats in the U.S. House of Representatives, according to the National Conference of State Legislatures and Election Data Services Inc., a political-consulting firm. Other states poised to gain at least one seat include Arizona, Nevada, Georgia, Florida and Utah.

Growth in these states is driven by factors including migration from other states, immigration and birth rates. The economic crisis has put the brakes on some of this expansion -- Florida just reported its first year-over-year population decline since 1946 -- but in general, Sun Belt states have grown faster than others over the past decade.

Since the number of seats in the House is capped at 435, the gains in the South and West have to be offset by losses elsewhere.

New York, New Jersey and Massachusetts and the recession-battered industrial states of Michigan, Ohio and Pennsylvania each stand to lose a House seat. So does Louisiana, where the population still hasn't rebounded from Hurricane Katrina in 2005, which displaced so many residents that census takers face a difficult task in tallying them all.

A state's votes in the presidential Electoral College depend on the size of its congressional delegation, so the census will likely tilt the balance of power slightly, with reliably Republican "red states" gaining several votes while Democratic strongholds such as New England lose clout.

The effect in Congress is less clear, said Karl Eschbach, the Texas state demographer. Texas, for instance, is solidly red when it comes to presidential elections. But Democrats have begun to make inroads in the state Legislature, buoyed by a flow of newcomers from more-liberal states such as California. So political analysts believe one or more of Texas's new seats in Congress may well translate into a Democratic pickup.

But population counts do more than determine congressional seats. They also govern the distribution of nearly $400 billion a year in federal funds for health care, transportation, housing and dozens of other programs.

Before all these calculations can begin in earnest, heads must be counted. And the 2010 census looks to pose a greater challenge than those of decades past.

The wave of foreclosures has pushed hundreds of thousands of families out of stable homes with known addresses, making them more difficult to track down. Some people are living with friends, crowding into motel rooms, moving from one rental to the next or camping out in cars. "Are they going to catch those people?" asked Kimball Brace, president of Election Data Services.

Census employees recently spent months scouring every corner of the U.S. -- on horseback and by boat when necessary -- in a quest to identify all the places "where people live or could live," said Gabriel Sanchez, who directs the bureau's efforts in Texas, Louisiana and Mississippi.

Mr. Sanchez's job includes counting residents of the most remote shanty towns along the Texas-Mexico border -- places with no streets, let alone addresses -- and communities populated mostly by illegal immigrants "who do not want to be found by the government," he said.

The 2010 Census will cost a record $14 billion, which includes some unprecedented steps to reach immigrants, both legal and not.

For the first time, the bureau will mail census forms in Spanish to 13 million households. It is buying television, radio, print or online ads in 28 languages (up from 17 in 2000), among them Dinka, spoken in south Sudan; Khmer, spoken in Cambodia; Teochew, spoken in parts of China and other Asian nations; and Wolof, spoken in Senegal.

This year's form will be among the shortest in history, with just 10 questions, to make it less intimidating.

No questions will address respondents' legal standing to live in the U.S. In decades past, citizenship status was asked on the long-form census, which went to a sampling of households, but that form was discontinued this year because the Census Bureau already gathers much of the information in separate community surveys.

Some critics of the census are angry about the lack of any attempt -- this year or in years past -- to classify undocumented immigrants separately. They carry the same weight as anyone else when congressional districts are redrawn even though they can't vote.

"United States citizens in one state should not be losing representation in Congress to illegal aliens in another state," said Ira Mehlman, a spokesman for the Federation for American Immigration Reform, which advocates tougher measures to stem illegal immigration.

His group calculates that if the undocumented were left out in 2010, California, Texas, Arizona and Florida would all lose seats while Midwestern states such as Indiana, Iowa, Michigan and Missouri would gain.

Write to Stephanie Simon at stephanie.simon@wsj.com